Electronic time-delay system



March 25, 1952 H. F. MAYER ELECTRONIC TIME-DELAY SYSTEM Filed Feb. 28,1951 Figl.

TIME- Inventor. Harry F. Mayer,

His Attorney.

POTENTIAL O POTENTIAL 0 CURRENT 0 Patented Mar. 25, 1952 ELECTRONICTIME-DELAY SYSTEM Harry F. Mayer, Baldwinsville, N. Y., assignor toGeneral Electric Company, a corporation of New York Application February28, 1951, Serial No. 213,171

2 Claims.

My invention relates to electronic tim delay systems and, moreparticularly, to such systems as may. be employed to delay a givenelectrical response for a specified time from the instant of actuation.

It is a primary object of my invention to provide an improved electronictime delay system to be used in connection with reduced voltage motorstarting processes, automatically delayed application of anode voltagefrom the instant of energization of heater elements for certain types ofvacuum tubes, and similar processes utilizing a time delay.

It is another object of my invention to provide an electronic time delaysystem which affords measured time delays of relatively long duration.

It is still another object of my invention to provide such a time delaysystem employing inexpensive and readily obtainable components.

In carrying out my invention, I provide an electronic circuit which, ineffect, increases the time constant, (1. e., the product of resistanceby capacitance) of a resistance-capacitance circuit by two separateoperations acting together. A charged capacitor is thus made todischarge at a much lower rate than would be established for the givenresistor-capacitor parameters and the slowly changing voltage across thecapacitor is amplified and used when it reaches a predeterminedmagnitude to cause proper actuating current to flow through a loaddevice such as a vacuum discharge device and a relay coil in series.Thus, the relay contacts are operated at some definite time after thecondenser is started to discharge, such time being considerably delayedby the action of my circuit.

The features of my invention which I believe to be novel are set forthwith particularity in the appended claims. My invention itself, however,together with iurther objects and advantages thereof, may best beunderstood by reference to the following description taken in connectionwith the accompanying drawing. In the drawing, Fig. 1 is a schematiccircuit diagram illustrating a preferred embodiment of my invention; andFig. 2 is a set of curves, drawn to a common time scale, illustratingthe potential variation at two points in the circuit and also acapacitor discharge current variation during the operation of theinvention.

Referring now to Fig. 1, I have shown a pre-- ferred circuit embodyingmy invention and including a source of alternating current and voltage Iand source of positive and negative unidirectional potential, suitablyrepresented by two rectifiers 2 and 3 together with two filteringcapacitors 4 and 5 connected as a full wave rectifier to the source I.For convenience, I have indicated that one side of source I is grounded,and have assumed for reference purposes that 2 grounded points remain atzero potential. Thus, the full wave rectifier establishes and maintainsa positive unidirectional supply potential on conductor 6 and a negativeunidirectional supply potential on conductor I when a switch 8, inseries with source I,is closed.

An electron discharge device, such as a vacuum tube triode 9, has itsanode I0 connected to conductor B through a resistor II and its cathodel2 connected to ground. A second electron discharge device, such as avacuum tube triode I3, has its anode I4 connected to conductor 6 and itscathode I 5 connected to conductor 7 through two cathode resistors I6and il in series. The junction point between resistors I6 and Hisindicated as point I8 for convenience in the following explanation ofcircuit operation. The control electrode I9 of triode 9 is connectedthrough a resistor 20 to point I8 and a second connection is made fromthe anode l0 through a timing capacitor 2| and a timing resistor 22(which may be a variable resistor as shown) in series to point I8.Triode I3. and resistor IB in series serve as a means for dischargingthe capacitor 2| with'an efiectively increased time constant: andtriodejfl serves as a second means, operative during the middle portionof the discharging cycle, for further increasing the effective timeconstant and reducing the rate of decay of discharge current fromcapacitor 2 I.

The control electrode 23 of triode I3 is connected to the junction pointbetween capacitor 2i and resistor 22 and also to the negative voltagesupply conductor 1 through a switch 24. Another electron dischargedevice, shown by way of example as a screen grid thyratron 25, is connected serially from its anode 26 through a load device illustrated asthe coil 21a of a relay 2! to the ungrounded side of source I. Toessentially eliminate chatter of relay 21, a capacitance 28 is connect din parallel with coil 21a. A control electrode 29 of thyratron 25 isconnected through a current limiting resistor 30 to point, I8, and thecathode 3| and screen grid electrode 32 are connected to the junctionpoint of two biasing resistors 33 and 34 which are in series with thesource I.

Relay 21 is provided with two normally open contacts 21b and 210.adapted to be closed upon the energization of coil 21a. The contacts 21band 210 are connected to some utilization circuit (not shown) which isto be completed after a specified time delay from the instant of actua+tion, which is the instant at which switch 24 is opened, as will behereinafter explained.

The heater elements 35, 36, and 31 of the respective tubes 9, I3, and 25may be supplied with power from a suitable step-down transformer 38 withits primary winding connected in series with source I, as shown. a

3 For an explanation of the operation of the circuitgaassume: thatswitch 3 is: closed andsthat conductors G and Tare maintained, byrectifiers 2 and 3, at respectively positive and negative unidirectionalpotentials with respect to ground;

The heater elements of the various vacuum tubes are properly heated bypowersupplied'fron'i the energized transformer 38. Further, assumeHt-hatswitch 24 is initially olosed so thatcontrolelectrode 23 is at thenegative potential of conductor I. The cathode followeraction.ofresistors I6 and I! thus limits the anode currentthrough triode I3 toa very small value, since ai-small amount of such current flowing drivescathode I5 :positivezin potential with respect to. control. elec-'-::trode 23... The.zanodesvoltage. .across. triode .13 is, rthereforesllghtly. .less.. .than V the .voltagesbetween conductors fisarrdl;.and..th -.po.tential atpoint I8 is ahighly inegativelbeing almostthesamepotential as that of conductor 1.. iSince no. current is'.;.-'flowing..through. resistors Ziland' 30,...control.elecs.-trodes..-I9-..and- 29.are atthesame negative potential was. pointI 8 so .that triode I 9 and thyratron 1225 eare cut off fromanode...current .flowl there- "i'through. .rCOil 21a is thusde-energized and con-' tactsz21bzand 210s are in the open position. Ca-

s-pacitor 2 I is charged. to the vfullivoltage between .conductorsfi andI and was .qui'cklyl charged to .thatz voltage by transient. currentflow through re- ..usistance II: and switch 'M after switcht is closed.Now assumethat actuation, i. el the opening .-.-.of=.-switch-24,- occursat time t=0."..Capacito'r 2| piano. longer maintained charged, and as itstarts -.-to. :discharge throughthe anode-cathode :path of trioderlfllthe poten-tial. oi electrode 23 approaches "masymptotically.thepotentialof point. I8. .How-

"-ever,.atheapotentia1 of point I B. does not :remain 1-.fixed; foraas;the. potential of. electrode 1 23. rises, anode :lcurrentthrough triodeI 3 increases and the 'rpotential. o f..point-larisessto only a.slightly lesser degree than .thes potential. of electrode v2 3, idu'eltorthe increasin voltage drop across resistor --I1.@Thedischargecurrent, indicated by .the arrow is in Fig. 1 flowingthroughresistor I I1, trirode- I 3; resistorv I5, .andresistor. 22,produces a a :voltage drop across timing resistor 22Iwhich holds rthe.risaof potential-at..electrode- 23 to. a. low irate.v...Thus,.=the.discharge which makes the potential of controlelectrodef23 approach asymptot- .icallyrthepotentialof point. I8 is suchthat timing capacitor-2| is discharging. toward a continually recedinggoal, .with. the resul'twthat the dis- 1 :chargingprocess takes muchlonger than it would otherwise. ..,.In. fact, -the timeconstant of the.discharge ismultipliedapproximately by the am-' plificationrfactori oftriode l3. The-variation of potentiallat.point I8.iswillustrated bycurve 39 v.irl .Fig. 2,. and the firstphase of operation just....described.occurs .theportion of the curv be- .tween time=.and.time=t1.

The potential variation at the anode IE) of trivMode 9 isillustrated bycurve 30 inFig. 2. During thefirst phase otoperatiomthe decreasingcharge won-capacitance 2|. causes thepotential of anode .1 0 .110. .drop-very. slightly,..as..shown in. curve 40. .The. time variation ofdischarge current is is il- .lustratedby-ucurve Min Fig. 2... .Itwillbeseen that; the. capacitor. 21 discharges .in essentially aretarded--.exponential.-- manners between the. -innstants time=0andtin1e=t1....However, durin the "1 :period between the instantstime tland-time=tz the dischargecurrent id issustainecl, i. e., its. rate -=tofexponential decay is lessened, and. thepotential at point I8 (curve 39)risesveryvery slowly, as hereinafter explained.

4 Now at the instant when time=t1, the potential at point 18, and thus.thepotential of con- .i trolelectrode I9, becomes 01.511011 avalue thatanode current begins to flow and to increase slow- :1 1y through triode9, causing an increasing voltage drop across resistor II and driving theanode II] I and the positive side of capacitor 2I increasinglyTlesspositive inpotential. The discharge current idiSthuS sustained andprevented from material- 1y decreasing but this, in turn, holds controlelectrode 23 at a negative potential with respect to cathode I5 so thatthe increase of current through -.resisto r I1 and the positive growthof potential at point I8 is considerably retarded. This is the secondphase ,of operation and .occurs between L v.time=t1 and timer-ties shownin Fig. 2.

Expressed another way,. the capacitance looking v.into capacitor 2i fromthe iuncti'onfofcapacitor 2i and resistorl? is substantially equal to.the capacitance of capacitor 2 I. multiplied by the control' electrodeto. anode gain'of' triode 9..;,The equality would be exact if resistorI6 were'ishortcircuited. 'The'efie'ctive resistance lookinginto re-.sistorZZ from. the junction oixcapacitor 2i and 25' resistor 22 isequal to theresistance'of resistor 22 multiplied by'th e' gain of triode'ISmeasured with the input between'control grid'andpoint Land .theoutputbetween point I8 and conductor I. Thus,'th'e circuit as a wholebetween the instants time=tr "and v time=tr "comprises. a"resistancecapacitance discharge "circuit in which the'actual timeconstant is efiectivelymultiplied by the gain of triode Band again bythe. gain of triode I3.

'When" the potential'at pointlBand at control 35. electrode '19. becomes.zero'at ti1ne'=.t2, control "ele'ctrcdecurrent starts to'fiow in triode9'."Ihus, the .potential'at ipoint I8 continues to grow positively th'epotential at control electrode I9 remains substantiallyconstant; due toa voltage 4o4drop1across resistor 26"causedby such''c011t1ol electrodecurrent. The; anode current: through "triode 9, "therefore;remainssubstantialiy constant, i; e;,-xthe-triode Qoeases'to produce anyamplification with respect topotential variation at-point I8, the'potential at anode It! remains substantially constant; and the'dischargecurrent is resumes a greater rate of decay; permitting a rapidrise of'anode'current through triode' I3; because of the decreasing voltagedrop across resistor 22, and a correspondingly rapid rise-of potentialat point" I8. 'This is shown on curve 39 "by the portion between time=t2and time :ts.

L'Ifhe potential at point 18,:and thus the potential at the'controlelectrode 280i thyratron 25, reachesa given positive'value at time: 153,such potential causing the thyratron 25 to conduct ...anode current,during positive half cycles'of its anode voltage suflicient to energizeload device .coil Z'Ea and close contacts 21b and 2'a'cv Thus, a delayperiod ,equal'to ts is interposed between the instant that switch 2 1 isopened and the .instant at which the contacts 27b and, 1210 are. closed.1

After time is, the anode. current through triode v..I.3 continues .toincrease slightly. andthenremains steadyat some higher value. ..The.thyratron 25 then. continues. to conduct anode. .current,-. on itspositivehalf cyclelof anode. voltage, so..that.contactsZ'Ib and 2'50.remain closed. When switch 2d isagain closed, the current throughitriodeI3 .decreases... to a very smallvvalue, capacitance 2| I .charges uptoitsnoriginal-voltage, tubes 9. and Ziarecut off,- contacts 211) and 21copen, and the.circuit is ready to repeat theactions hereinbeforedescribed.

The self-biasing resistor I5 is not essential to the circuit, but itsuse is desirable because it prevents control electrode current fromflowing in triode 3 as the end of the discharge of capacitance 2| isapproached. Any such control electrode current makes the effectiveresistance of resistor 22 smaller and reduces the biasing action ofdischarge current is.

The rectifiers 2 and 3 shown in Fig. 1 may be of the hot or cold vacuumdiode type, if desired," or of the copper oxide or selenium type. Ifrectifiers requiring no cathode heating time are used, however, the useof switch 24 is optional, since the closing of switch 8 may thenconstitute timing circuit actuation. That is, with switch 24 removedfrom the circuit or permanently opened, the rectifiers instantly applyunidirectional potentials to conductors 6 and 1 when switch 8 is closed.The capacitor 2| charges u to full voltage very quickly throughresistors 22, and I1 before the heater elements of the various vacuumdischarge devices become hot enough to permit anode current fiow; andwhen the heater elements do reach the proper temperature for anodecurrent fiow the operation of the circuit proceeds as hereinbeforedescribed from the instant that switch 24 is opened. Circuit actuationby this method, therefore, extends the time delays obtainable by thelength of time necessary to heat the heater elements and cathodessufiiciently for electron'emission therefrom.

My invention is not limited to the use of a thyratron for the tube 25but obviously includes the use of other vacuum discharge devices. Suchdevices may easily be connected, if desired, to the positive potentialconductor 6 to supply them with unidirectional anode voltage instead ofbeing connected across source I to receive an alternating anode voltagesupply. Further, my invention obviously includes the use of relaycontacts or other circuit-completing means in place of the manuallyoperated switches 8 and 26.

My electronic time delay system has been built and tested and found tooperate as hereinabove described. Merely by way of illustration and inno sense by way of limitation, I have found that the following circuitconstants may be employed for the elements of the circuit:

Source 115 volts, 400 cycles per sec. Rectifiers 2 and 3 selenium diodesCapacitors 4 and 5 0.10 microfarad Triode 9 one-half of a type 12AX'7duplex triode Resistor 1.0 megohm 'Iriode |3 one-half of a type 12AX7duplex triode Resistor i6 15,000 ohms Resistor 1.0 megohm Resistor 201.0megohm Capacitor 2| 0.25 microfarad Resistor 22 5.1 megohms(variable) Thyratron 25 type 2D21 thyratron Relay coil 21a 6500 ohms; m.a.

Resistor 30 1.0 megohm Resistor 33 39,000 ohms Resistor 34 4,300 ohmsTransformer 38---- 115/63 volts 400 cycles per sec.

The time delay obtainable using the above circuit constants was found tobe adjustable over a range from approximately zero to 4.5 minutes byvarying the value of resistor 22. It was further found that considerableadjustment of 6 the duration of time delay could be obtained by makingresistor l6 variable and adjusting its resistance to various values.

While I have shown and described a preferred embodiment of my invention,other embodiments and modifications will occur to those skilled in theart, and I intend to cover in the appended claims all such modificationsas fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. An electronic time delay system comprising a timing capacitor and atiming resistor in series; a first source of positive unidirectionaloperating potential and a second source of negative unidirectionaloperating potential; means for discharging said timing capacitor with aneffectively increased time constant comprising a first resistor and afirst electron discharge device having a first anode, a first cathode,and a first control electrode; said first resistor connecting said firstcathode and said second source, said first anode being connected to saidfirst source. said first control electrode being connected ,to thejunction point of said timing capacitor and said timing resistor, andsaid first cathode also being connected to the terminal of said timingresistor remote from said junction; means operative only during a middleportion of the discharge of said timing capacitor comprising a secondresistor, a third resistor, and a second electron discharge devicehaving a second anode, a second cathode and a second control electrode;said second resistor connecting said second anode and said first source,said third re sistor connecting said second control electrode and saidfirst cathode, said second anode being also connected to the terminal ofsaid timing capacitor remote from said junction, and said second cathodebeing connected to a point of zero potential; a third electron dischargedevice having a control electrode circuit and an anode circuit; a loaddevice connected in said anode circuit; and means for biasing saidcontrol electrode circuit in response to the voltage across said secondsource and said first resistor in series; the anode current in saidthird device being insufiicient to energize said load device until thevoltage across said first resistor rises to a predetermined value.

2. An electronic time delay system comprising a first electron dischargedevice having a first anode, a first cathode, and a first controlelectrode; a first source of positive unidirectional operating potentialconnected tosaid first anode; a second source of negative unidirectionaloperating potential; a first resistor and a second resistor connected inseries relationship between said first cathode and said second source,said first resistor being connected to said second source;. a secondelectron discharge device having a secondanode, a second cathode, and asecond control electrode; said second cathode connected to a point ofzero potential; a third resistor connecting said second anode and saidfirst source; a timing capacitor and a timing resistor seriallyconnected between said second anode and the junction of said first andsaid second resistors; said first control electrode being connected tothe junction of said timing capacitor and said timing resistor; a fourthresistor connected between-said second control electrode and thejunction point of said first and said second resistors; means removablyconnecting said first trode circuit and an'anQde circuit; aiihird;source 1-: -:-'of :opemting potential; and anload device said anodecircuit; and. means for;..biasing .;said; con-:- trolielectitodecircuit. in ,respnnse; 001 the .voltage across. saicbsecoind source-'and saidyfirsturesistor :in= series the anode currentv in 1 said thirddevice being insufficient to energize said-load device unv 'a til thevoltage across said 'firstcresistor rises to a. 10

predetermined-"value.

Hr-HARRY MAYER.

REEER'ENGESLLCITED The .folloWirig references are "ofrecord: irf'thefile j ofthis patient:

' "UNITED STATES PATENTS qNumber I Name @yDate "Mortley Apr.:.7,';1942Zepler V June. 30,1942 Kinsman Jan, 30,1945 Engelhardt N0v '26,..1946Schneider iMarv 1,;1919 Mayer V n.-- Feb. =14,41950

